The objective of this research proposal is a clarification of the mechanism of CA ions accumulation and Ca ions release in Sarcoplasmic Reticulum. Our specific aims include: (a) solubilization of membrane components, identification of the ATPase involved in Ca ions transport, and determination of its size and physical properties. (b) labelling of the ATPase enzymatic site, and characterization of peptidic fragments. (c) investigations on structural and conformations features of sarcoplasmic membranes and their components, in an attempt to discover physical phenomena that could account for ion translocation across the membrane. (d) attempts to reconstitute functioning membranes on suitable supports, dividing chambers accessible to chemical and electrical measurements. (e) rapid kinetics (milliseconds) of Ca ion accumulation and release. The work of Sarcoplasmic Reticulum is relevant to the understanding of contractile strength in cardiac and skeletal muscle, of its regulation in normal and abnormal states, and its control by appropriate pharmacological agents. In addition, Sarcoplasmic Reticulum is a suitable system where to study basic structural and functional features of ion pumps in biological membranes.